Delay locked loop circuit

ABSTRACT

A delay locked loop (DLL) circuit has a first delay line that delays a received external clock signal for a fine delay time and then outputs a first internal clock signal; a duty cycle correction unit that corrects a duty cycle of the first internal clock signal and then outputs a second clock signal; a second delay line that delays the second clock signal for a coarse delay time and then outputs a second internal clock signal; and a phase detection and control unit that detects the difference between the phases of the external clock signal and the fed back second internal clock signal, and controls the fine delay time and the coarse delay time. The DLL circuit performs coarse locking and fine locking by using different type delay cells, and thus consumes a small amount of power and robustly withstands jitter and variation in PVT variables.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority under 35 U.S.C. 119 to Korean PatentApplication No. 10-2006-0104029, filed on Oct. 25, 2006, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a delay locked loop (DLL) circuit, andmore particularly, to a DLL circuit that can operate at high speedswhile reducing power consumption.

2. Description of the Related Art

A DLL circuit is included in a semiconductor memory device to performphase adjustment so that an internal clock signal input to or outputfrom the DLL circuit can be synchronized with an external clock signal.A DLL performs signal synchronization by delaying a signal input to oroutput from the DLL according to an external clock signal via a delayline.

FIG. 1 is a circuit diagram of a conventional delay locked loop (DLL)circuit 100. Referring to FIG. 1, the DLL circuit 100 includes a delayline 101, a duty cycle correction (DCC) circuit 120, a phase detectionand control circuit 130, and a replica delay path 135.

The phase detection and control circuit 130 compares the phase of anexternal clock signal Ext_CLK with that of a corrected clock signalCCLK, and detects the phase difference between the external clock signalExt_CLK and the corrected clock signal CCLK based on the phase of theexternal clock signal Ext_CLK. Then the phase detection and controlcircuit 130 transmits information regarding the detected phasedifference to the phase mixer 150 so that the external clock signalExt_CLK can be delayed by the detected phase difference in the phasemixer 150.

The delay line 101 generates an internal clock signal Int_CLK bydelaying the external clock signal Ext_CLK for a predetermined amount oftime, in response to the output of the phase detection and controlcircuit 130. The delay line 101 includes a delay circuit 110 and a phasemixer 150.

The delay circuit 110 includes a plurality of delay cells 114, 116, . .. , 118, and generates a plurality of clock signals D_0 through D_n bydelaying the external clock signal Ext_CLK input to the delay circuit110 at regular intervals. Whenever the external clock signal Ext_CLKpasses through one delay cell, e.g., the delay cell 114, the externalclock signal Ext_CLK is delayed for a time t1 and then is output to thephase mixer 150. The delay circuit 110 can further include a buffer 112in front of the delay cells 114, 116, . . . , 118. Thus, the originalexternal clock signal Ext_CLK that is not delayed is output to the phasemixer 150 as a first delayed signal D_0, and the result of delaying theexternal clock signal Ext_CLK by a time t1 is output to the phase mixer150 as a second delayed signal D_1. If n delay cells are included, asignal generated by delaying the original external clock signal Ext_CLKby a time t1×n is output to the phase mixer 150 as an nth delayed signalD_n.

The phase mixer 150 receives the delayed signals D_0 through D_n fromthe delay circuit 110 and then selects one of the delayed signals D_0through D_n, for example, a delayed signal D_i, and outputs the delayedsignal D_i as the internal clock signal Int_CLK. The phase mixer 150 canbe a multiplexer.

The DCC circuit 120 cancels and corrects a duty cycle error present ineach received internal clock signal Int_CLK and then outputs a correctedclock signal CCLK whose duty cycle is maintained at a normal level (ingeneral, a signal having a duty ratio of 50%:50%. The DCC circuit 120includes an amplification unit 122, a charge pump 124, and adigital-to-analog converter (DAC) 126.

The amplification unit 122 adjusts the duty cycle of the internal clocksignal Int_CLK in response to a control signal VC output from the chargepump 124.

The charge pump 124 adjusts the voltage of the control signal VC inresponse to the corrected clock signal CCLK received via the replicadelay path 135.

The DAC 126 is installed in order to prevent duty cycle information frombeing erased in a power down mode of a memory device, such as a dynamicrandom access memory (DRAM). In the power down mode of a DRAM, powersupply to the DCC circuit 120 is discontinued. If power supply isdiscontinued, a self-refresh operation of a memory cell is stopped andthus information stored in the memory cell is likely to be erased due todischarge of a capacitor. Thus the DAC 126 transforms the duty cycleinformation memorized in a voltage format into a digital signal and thenstores the digital signal in order to prevent the duty cycle informationfrom being erased. That is, the duty cycle information is latched inorder to memorize it.

The replica delay path 135 compensates for a delay occurring in a firstpath PATH1 via which the corrected clock signal CCLK is transmitted froma first node N1 to a destination circuit (not shown) that actually usesthe corrected clock signal CCLK. The internal clock signal CCLK adjustedby the DLL circuit 100 for signal synchronization is delayed againduring movement to the destination circuit that actually uses theinternal clock signal CCLK. Thus, the replica delay, path 135 isincluded in order to compensate for the delay in the first path PATH1.The phase of a delayed corrected clock signal CCLK_D is the same as thatof a clock signal CLK_out transmitted to the destination circuit. Thereplica delay path 135 includes a plurality of delay cells (not shown)causing a delay equivalent to the delay occurring in the first pathPATH1.

In the case of the conventional DLL circuit 100, the external clocksignal Ext_CLK is first transmitted to the phase detection and controlcircuit 130. The phase detection and control circuit 130 compares thephases of the external clock signal Ext_CLK and the fed back delayedcorrected clock signal CCLK_D and the phase difference therebetween.Information regarding the detected phase difference is transmitted tothe phase mixer 150 in the delay line 101. The delay line 101 adjusts arough delay, i.e., it performs coarse locking, according to the receivedinformation regarding the phase difference. Through rough delayadjustment (first delay), the internal clock signal Int_CLK approximatesthe external clock signal Ext_CLK.

If the internal clock signal Int_CLK on which coarse locking has beenperformed passes through the DCC circuit 120, the duty cycle of theinternal clock signal Int_CLK is corrected and then output as thecorrected clock signal CCLK. The corrected clock signal CCLK passingthrough the replica delay path 135 is delayed for the delay time in thefirst path path1. The phase detection and control circuit 130 comparesthe delayed corrected clock signal CCLK_D with the original externalclock signal Ext_CLK and detects a fine delay time (second delay).Information regarding the detected fine delay time (second delay) istransmitted to the phase mixer 150. The phase mixer 150 precisely delaysthe external clock signal Ext_CLK for the detected fine delay time(second delay) and outputs a precisely adjusted internal clock signalInt_CLK.

The precisely adjusted internal clock signal Int_CLK is delayed by thereplica delay path 135 and then is fed back to the phase detection andcontrol circuit 130. The phase detection and control circuit 130compares the internal clock signal Int_CLK that was precisely adjustedand delayed with an external clock signal. If the internal clock signalInt_CLK coincides with the external clock signal, the delay line 101discontinues signal delay.

FIG. 2 is a circuit diagram illustrating the conventional delay cells114, 116, 118 illustrated in FIG. 1. Referring to FIG. 2, each of theconventional delay cells 114, 116, . . . , 118 includes an even-numberedplurality of inverters 201 connected in series. The original signalinput to the delay cells 114, 116, 118 is delayed while passing throughthe chain of two or even-numbered inverters 201 connected in series ineach of the conventional delay cells 114, 116, . . . , 118, and then isoutput. The conventional delay cells 114, 116, . . . , 118, beinginverter chain-type delay cells, have an advantage of consuming lesspower than other type delay cells, e.g., differential amplifier typedelay cells. The type of the conventional delay cells 114, 116, . . . ,118 is not limited. For example, the conventional delay cells 114, 116,. . . , 118 can be delay cells (not shown) using differentialamplifiers.

A conventional DLL performs coarse locking and fine locking by usingdelay cells, such as the delay cells 114, 116, . . . , 118.

However, all n delayed signals D_1 through D_n that are respectivelyoutput from the conventional delay cells 114, 116, . . . , 118 aresupplied to the phase mixer 150 of FIG. 1. Here, n is a large value thatis precisely determined according to a maximum signal delay time. Thus,the more complex the relationship among signals that are input to andoutput from the phase mixer 150, the greater the signal loading is.

Accordingly, in the case of the conventional DLL circuit 100 illustratedin FIG. 1 that uses inverter type delay cells, power consumption can bereduced but signal loading is increased. Also, the signal mixingperformance of the phase mixer 150 is degraded, thus increasing jitterin a plurality of delayed signals D_i. Also, the inverter type delaycells are greatly influenced by signal change caused by variation inpower, voltage, and temperature (PVT) variables.

In general, the faster a DRAM operates, the greater the jitter. However,a DRAM operating at high speeds must have a small jitter value in orderto precisely transmit data. Thus the extent of jitter must be reduced.

A delay cell using differential amplifiers is constructed by connectingdifferential amplifiers in series and thus can effectively combat jitterand can robustly withstand variation in the PVT variables. Accordingly,a delay cell using differential amplifiers can be used instead of theinverter type delay cell that has a delay jitter problem and issignificantly affected by variation in the PVT variables.

However, the differential amplifier type delay cell consumes a largeamount of power. Also, since the relationship among signals that areinput to and output from the delay cell is complex, the signal loadingon the delay cell is increased. Accordingly, the high-speed operation ofa semiconductor device, such as a DRAM, is limited.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a delaylocked loop (DLL) circuit that is capable of performing coarse lockingand fine locking by using different type delay cells, and thus consumesa small amount of power, effectively combats jitter, and robustlywithstands variation in power, voltage, and temperature (PVT) variables.

According to an aspect of the present invention, provided is a delaylocked loop circuit comprising: a first delay line configured to delay areceived external clock signal for a fine delay time and then output afirst internal clock signal; and a second delay line configured to delaythe second clock signal for a coarse delay time and then output a secondinternal clock signal, wherein the first delay line and the second delayline are sequentially arranged, and the second clock signal is generatedusing the first internal clock signal.

A delay cell of the first delay line can comprise a differentialamplifier.

A delay cell of the second delay line can comprise an inverter.

The delay locked loop circuit can further comprise a phase detection andcontrol unit configured to detect a difference between the phases of theexternal clock signal and the fed back second internal clock signal, andto control the fine delay time and the coarse delay time.

The delay locked loop circuit can further comprise a replica delay patharranged between an output terminal of the second delay line and thephase detection and control unit, and configured to compensate for adelay occurring during transmission of the second internal clock signalto a target circuit which uses the second internal clock signal.

The first delay line can include a number of delay cells in a range of 2through 5.

An ith delay cell in the first delay line can comprise: a firstdifferential amplifier configured to respectively receive the (i−1)thfinely delayed signal output from an (i−1)th delay cell in the firstdelay line and an inverted signal of the (i−1)th finely delayed signalvia two input terminals of the first differential amplifier,differentially amplify the (i−1)th finely delayed signal and theinverted signal of the (i−1)th finely delayed signal, and then outputthe amplified signals; and a second differential amplifier configured torespectively receive the amplified signals from both output terminals ofthe first differential amplifier via two input terminals of the seconddifferential amplifier, differentially amplify the amplified signals,and then output the ith finely delayed signal and an inverted signal ofthe ith finely delayed signal via both output terminals of the seconddifferential amplifier, wherein the first and second differentialamplifiers operate in response to a first selection signal.

The phase detection and control unit can be configured to perform aphase comparison to determine if the first selection signal is at alogic high or logic low.

The first differential amplifier of the ith delay cell can comprise: afirst MOS transistor having a drain connected to a power supply sourceconfigured to supply a high voltage, and configured to receive the(i−1)th finely delayed signal via a gate thereof; a first inversion MOStransistor having a drain connected to the power supply source, andconfigured to receive the inverted signal of the (i−1)th finely delayedsignal via a gate thereof; a first selection MOS transistor having adrain connected to a source of the first MOS transistor, and configuredto receive the first selection signal via a gate thereof; and a firstbias transistor having a drain connected to the first selectiontransistor and a source connected to a ground voltage source, andconfigured to receive a first bias signal via a gate thereof. The seconddifferential amplifier of the ith cell of the first delay cells cancomprise: a second MOS transistor having a drain connected to the powersupply source and a gate connected to the drain of the first MOStransistor, and configured to output the ith finely delayed signal viathe drain of the second MOS transistor; a second inversion MOStransistor having a drain connected to the power supply source and agate connected to the drain of the first inversion MOS transistor, andconfigured to output the inverted signal of the ith finely delayedsignal via the drain of the second MOS transistor; a second selectionMOS transistor having a drain connected to the source of each of thesecond MOS transistors, and configured to receive the first selectionsignal via a gate of the second selection MOS transistor; and a secondbias transistor having a drain connected to the source of the secondselection MOS transistor and a source connected to the ground voltagesource, and configured to receive the first bias signal via a gate ofthe second bias transistor.

The first bias signal can be supplied in order to bias the first andsecond differential amplifiers.

The first differential amplifier of the ith delay cell further cancomprise: a first resistor connected between the drain of the first MOStransistor and the power supply source; and a second resistor connectedbetween the drain of the first inversion MOS transistor and the powersupply source. The second differential amplifier of the ith cell of thefirst delay cells can further comprise: a third resistor connectedbetween the drain of the second MOS transistor and the power supply; anda fourth resistor connected between the drain of the second inversionMOS transistor and the power supply source.

The first delay line can comprise: a first delay circuit including ndelay cells connected in series; and a phase mixer configured to selectat least one of the external clock signal and first through nth finelydelayed signals and then output a signal generated by using the selectedsignal as the first internal clock signal, in response to informationregarding the detected phase difference and an output of the phasedetection and control unit.

The phase mixer can comprise a multiplexer.

A kth delay cell in the second delay line can comprise: a first inverterconfigured to receive a signal output from a (k−1)th delay cell; and asecond inverter having an input terminal connected to an output terminalof the first inverter, and configured to output a kth coarsely delayedsignal via an output terminal thereof.

The delay locked loop circuit of claim 14, wherein the kth delay cellcan comprise: the first inverter having an input terminal connected toan output terminal of a second inverter of the (k−1) cell of the seconddelay cells, and an output terminal connected to the input terminal ofthe second inverter of the kth cell of the second delay cells; thesecond inverter configured to output the kth coarsely delayed signal viaan output terminal thereof; a first inversion selection transistorhaving a first terminal connected to the power supply source and asecond terminal connected to a first bias terminal of the firstinverter, and configured to receive an inverted signal of the secondselection signal via a gate thereof; a first selection transistor havinga first terminal connected to a second bias terminal of the firstinverter and a second terminal connected to the ground voltage source,and configured to receive the second selection signal via a gatethereof; a second inversion selection transistor having a first terminalconnected to the power supply source and a second terminal connected toa first bias terminal of the second inverter, and configured to receivethe inverted signal of the second selection signal via a gate thereof;and a second selection transistor having a first terminal connected to asecond bias terminal of the second inverter and a second terminalconnected to the ground voltage source, and configured to receive thesecond selection signal via a gate thereof.

The first and second inverters can be configured to operate in responseto a second selection signal.

The phase detection and control unit can be configured to perform aphase comparison to determine if the second selection signal is at alogic high or logic low.

The delay locked loop circuit can further comprise a duty cyclecorrection unit configured to correct a duty cycle of the first internalclock signal and then output a second clock signal.

The duty cycle correction unit can comprise: a charge pump configured tooutput a control signal configured to correct a duty cycle of the firstinternal clock signal to an amplification unit, in response to thesecond internal clock signal; the amplification unit configured tocompensate for the duty cycle of the first internal clock signal and tooutput the corrected signal, in response to the control signal; and adigital-to-analog converter configured to transform informationregarding a duty cycle of the second internal clock signal into adigital signal and then store the digital signal, for a memory devicepower down mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent in view of the attacheddrawings and accompanying detailed description. The embodiments depictedtherein are provided by way of example, not by way of limitation,wherein like reference numerals refer to the same or similar elements.The drawings are not necessarily to scale, emphasis instead being placedupon illustrating aspects of the invention. In the drawings:

FIG. 1 is a block diagram of a conventional delay locked loop (DLL)circuit;

FIG. 2 is a detailed circuit diagram of delay cells of the DLL circuitillustrated in FIG. 1;

FIG. 3 is an embodiment of a block diagram of a DLL circuit according toan aspect of the present invention;

FIG. 4 is a detailed circuit diagram of an embodiment of a first delaycell included in a first delay line of the DLL circuit illustrated inFIG. 3, according to an aspect of the present invention;

FIG. 5 is a detailed circuit diagram of an embodiment of a second delaycell included in a second delay line of the DLL circuit illustrated inFIG. 3, according to an aspect of the present invention; and

FIG. 6 is a graph illustrating the result of an experiment comparing theamount of current consumed in a DLL circuit according to the presentinvention with the amount of current consumed in a conventional DLLcircuit.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, aspects of the present invention will be described byexplaining illustrative embodiments in accordance therewith, withreference to the accompanying drawings. Like reference numerals denotelike elements throughout the drawings.

It will be understood that, although the terms first, second, etc. arebe used herein to describe various elements, these elements should notbe limited by these terms. These terms are used to distinguish oneelement from another, but not to imply a required sequence of elements.For example, a first element can be termed a second element, and,similarly, a second element can be termed a first element, withoutdeparting from the scope of the present invention. As used herein, theterm “and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that when an element is referred to as being “on”or “connected” or “coupled” to another element, it can be directly on orconnected or coupled to the other element or intervening elements can bepresent. In contrast, when an element is referred to as being “directlyon” or “directly connected” or “directly coupled” to another element,there are no intervening elements present. Other words used to describethe relationship between elements should be interpreted in a likefashion (e.g., “between” versus “directly between,” “adjacent” versus“directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like may be used to describe an element and/or feature'srelationship to another element(s) and/or feature(s) as, for example,illustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thedevice in use and/or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” and/or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.The device may be otherwise oriented (e.g., rotated 90 degrees or atother orientations) and the spatially relative descriptors used hereininterpreted accordingly.

FIG. 3 is a block diagram of a delay locked loop (DLL) circuit 300according to an aspect of the present invention. Referring to FIG. 3,the DLL circuit 300 includes a first delay line 301, a duty cyclecorrection (DCC) unit 320, a second delay line 330, a phase detectionand control unit 340, and a replica delay circuit 350.

The operations and structure of the DCC unit 320 and the replica delaycircuit 350 are the same as those of the DCC unit 120 and the replicadelay circuit 135 of the conventional DLL circuit 100 illustrated inFIG. 1 and thus a detailed description thereof will not be providedhere.

The phase detection and control unit 340 compares the phase of anexternal clock signal Ext_CLK with that of a second internal clocksignal Int_CLK2 that is fed back to the phase detection and control unit340, and detects the phase difference therebetween. Then the phasedetection and control unit 340 outputs a delay control signal DCON thatis determined to be logic high or logic low depending on the detectedphase difference. For example, a user can set a delay control signalDCON that goes high to be output when delay adjustment is needed due toa phase imbalance. Here, the phase detection and control unit 340transmits a phase difference signal DLi to the phase mixer 305. Thephase difference signal DLi contains information regarding the phasedifference.

The first delay line 301 includes a first delay circuit 310 and a phasemixer 305. The first delay line 301 delays the external clock signalExt_CLK for a predetermined delay of time and then outputs it, inresponse to a signal received from the phase detection and control unit340. Here, the predetermined delay of time is a time required to performfine locking.

The first delay circuit 310 includes a plurality of first delay cells314, 316, 318 connected in series. The first delay circuit 310 canfurther include a buffer 312 in front of the first delay cells 314, 316,. . . , 318. Here, the external clock signal Ext_CLK before it has beendelayed will be referred to as a 0th finely delayed signal D_0, and asignal output from the ith cell will be referred to as an ith finelydelayed signal D_i.

The ith finely delayed signal D_i is delayed for a time t1 and thenoutput to the phase mixer 305 whenever it passes through one of thefirst delay cells 314, 316, . . . , 318. Thus, if n first delay cells314, 316, . . . , 318 are present, an nth finely delayed signal D_n thatis obtained by delaying the external clock signal Ext_CLK for a timet1×n is output to the phase mixer 305.

The first delay circuit 310 is used to perform fine locking. It ispossible to perform fine locking even using a small number of delaycells since a delay time for fine locking has a small value. Thus, thetotal number of delay cells in the first delay circuit 310 is less thanin the second delay circuit 330, which will be described later. Thetotal number of first delay cells included in the first delay circuit310 can be 2 or 3, for example. The phase mixer 305 selects one of aplurality of finely delayed signals D_i received from the first delaycircuit 310 and then outputs the selected signal. The signal output fromthe phase mixer 305 is referred to as a first internal clock signalInt_CLK1.

For example, if the phase of the second internal clock signal Int_CLK2fed back to the phase detection and control unit 340 advances the phaseof the external clock signal Ext_CLK by the time t1, the phase mixer 305selects and outputs a first finely delayed signal D_1. If the differencebetween the phases of the fed back second internal clock signal Int_CLK2and the external clock signal Ext_CLK is not a multiple of the time t1,the phase mixer 305 mixes the finely delayed signals D_i and thenoutputs the mixing result. The construction and operation of the firstdelay cell 314 will later be described in detail with reference to FIG.4.

The DCC unit 320 corrects the duty cycle of the first internal clocksignal Int_CLK1 and then outputs a second clock signal IN2.

The second delay line 330 includes a plurality of second delay cells332, 334, . . . , 336. The second delay line 330 receives the secondclock signal IN2, delays it according to coarse locking, and thenoutputs the second internal clock signal Int_CLK2. For coarse locking,an additional phase mixer is not needed, since delay adjustment is notfinely performed and thus mixing of delayed signals is not needed andthe amount of delay can be controlled in response to a second selectionsignal SEL2 (see FIG. 5) that is input under control of the phasedetection and control unit 340.

If the total number of the second delay cells 332, 334, . . . , 336 inthe second delay line 330 is n, an ith second delay cell from among then second delay cells 332, 334, . . . , 336 receives and delays an(i−1)th coarsely delayed signal DCO_(i−1) and then outputs an ithcoarsely delayed signal DCO_i. For example, the first cell 332 receivesthe second clock signal IN2 and outputs the first coarsely delayedsignal DCO_1, and the nth cell 336 receives the (n−1)th coarsely delayedsignal DCO_(n−1) and outputs an nth coarsely delayed signal DCO_n. Theconstructions and operations of each of the second delay cells 332, 334,. . . , 336 will be described later in detail with reference to FIG. 5.

First, the phase detection and control unit 340 compares the phase ofthe external clock signal Ext_CLK with that of the fed back secondinternal clock signal Int_CLK2 and then detects the phase differencetherebetween. If a phase difference is present, the DLL circuit 300begins to operate and then the phase detection and control unit 340transmits the phase difference signal DLi containing the informationregarding the phase difference to the phase mixer 305.

The first delay line 301 receives the external clock signal Ext_CLK anddelays the external clock signal Ext_CLK for a constant delay time thatis not related to the phase difference signal DLi. That is, fine lockingis not performed. The constant delay can be variously set by a user, andcan be set to a value of 0 so that the external clock signal_Ext_CLK isoutput without being delayed. In order not to allow the second delayline 330 to perform fine locking before coarse locking, first, the firstdelay line 301 creates a signal that is not delayed or is delayed forthe constant delay time and then outputs the first internal clock signalInt_CLK1.

Also, the DCC unit 320 corrects the duty cycle of the first internalclock signal Int_CLK1 and outputs the second clock signal IN2. Then thesecond delay line 330 performs coarse locking based on the phasedifference signal DLi received from the phase detection and control unit340 (although not shown in FIG. 3, it would be apparent to those ofordinary skill in the art that the phase difference signal DLi can bedirectly transmitted to the second delay line 332 or transmitted via thefirst delay line 301 and the DCC unit 320).

The second internal clock signal Int_CLK2 output by performing coarselocking is fed back to the phase detection and control unit 340 via thereplica delay circuit 350. Then the phase detection and control unit 340precisely computes a delay time and transmits the phase differencesignal DLi to the phase mixer 305. Thereafter, the first delay line 301performs fine locking on the external clock signal Ext_CLK.

FIG. 4 is a detailed circuit diagram of an embodiment of the first delaycell 314 from among the first delay cells 314, 316, . . . , 318 includedin the first delay circuit 310 of the DLL circuit 300 illustrated inFIG. 3. The construction and operation of each of the first delay cells314, 316, . . . , 318 will now be described with respect to the firstdelay cell 314, as an example.

Referring to FIG. 4, the first delay cell 314 includes first and seconddifferential amplifiers 410 and 430. The first differential amplifier410 includes a pair of first resistors 411 and 413, a pair of first MOStransistors M1_1 415 and M1_2 417, a first selection MOS transistor M_S1419, and a first bias transistor M_BIAS1 421. The second differentialamplifier 430 includes a pair of second resistors 431 and 433, a pair ofsecond MOS transistors M2_1 435 and M2_2 437, a second selection MOStransistor M_S2 439, and a second bias transistor M_BIAS2 441.

In the first differential amplifier 410, a first terminal of the firstresistor 411 is connected to a high voltage source V_DD and a secondterminal thereof is connected to a first node N1. A first terminal ofthe first MOS transistor M1_1 415 is connected to the first node N1 anda second terminal thereof is connected to a fifth node N5. A firstterminal of the first resistor 413 is connected to the high voltagesource V_DD and a second terminal thereof is connected to a second nodeN2. A first terminal of the first MOS transistor M1_2 417 is connectedto the second node N2 and a second terminal thereof is connected to thefifth node N5.

The drain and source terminals of the first selection MOS transistorM_S1 419 are respectively connected to the fifth node N5 and a seventhnode N7, and a first selection signal SEL1 is supplied to the gateterminal thereof. The drain and source terminals of the first biastransistor M_BIAS1 421 are respectively connected to the seventh node N7and a ground voltage source V_GND, and a first bias signal VBIAS1 issupplied to the gate terminal thereof.

The first differential amplifier 410 respectively receives a first inputsignal IN and an inverted signal INB of the first input signal via thegate terminals of the first MOS transistors M1_1 415 and M1_2 417,differentially amplifies the first input signal IN and the invertedsignal INB, and then outputs the amplified signals. The amplifiedsignals cannot be output unless a first selection signal SEL1 that goeshigh is applied to turn on the first selection MOS transistor M_S1 419.

In the second differential amplifier 430, a first terminal of the secondresistor 431 is connected to high voltage source V_DD and a secondterminal thereof is connected to a third node N3. A first terminal ofthe second resistor 433 is connected to high voltage source V_DD and asecond terminal thereof is connected to a fourth node N4. A firstterminal of the second MOS transistor M2_1 435 is connected to the thirdnode N3 and a second terminal thereof is connected to a sixth node N6. Afirst terminal of the second MOS transistor M2_2 437 is connected to thefourth node N4 and a second terminal thereof is connected to the sixthnode N6.

The drain and source terminals of the second selection transistor M_S2439 are respectively connected to the sixth node N6 and an eighth nodeN8, and the first selection signal SEL1 is supplied to the gate terminalthereof. The drain and source terminals of the second bias transistorM_BIAS2 441 are respectively connected to the eighth node N8 and groundvoltage source V_GND, and a first bias signal VBIAS1 is supplied to thegate terminal thereof.

A first finely delayed signal D_1 is output from the drain of the secondMOS transistor M2_1 435. An inverted signal DB_1 of the first finelydelayed signal D_1 is output from the drain of the second MOS transistorMS_2 437. The first finely delayed signal D_1 is transmitted to theinput terminal of a first differential amplifier (not shown) of thesecond first delay cell 316. The inverted signal DB_1 of the firstfinely delayed signal D_1 is transmitted to the inversion input terminalof the first differential amplifier of the second first delay cell 316.

A certain amount of time is incurred for the first input signal IN andthe inverted signal INB to be supplied to both the input terminals offirst differential amplifier 410 and for the signals D_1 and DB_1 to beoutput from the second differential amplifier 430. Thus, the first delaycell 314 operates as delay cell by using the input and outputcharacteristics of the differential amplifiers 410 and 430.

Here, the logic level of the first selection signal SELL is determinedaccording to the result of phase comparison performed by the phasedetection and control unit 340 illustrated in FIG. 3. If the phases ofthe external clock signal Ext_CLK and the fed back second internal clocksignal Int_CLK2 are the same, the first selection signal SEL1 that goeshigh is applied, thus deactivating the first delay cell 314. If thephases of the external clock signal Ext_CLK and the fed back secondinternal clock signal Int_CLK2 are different from each other and thusthe external clock signal Ext_CLK must be delayed, the first selectionsignal SELL that goes high is applied, thus activating the first delaycell 314.

The first bias signal VBIAS is a signal that a user inputs in order tobias the first and second differential amplifiers 410 and 430. Ingeneral, the operating characteristics of a circuit within asemiconductor device are influenced by variation in power and voltageapplied to the circuit and the temperature of the semiconductor device(power, voltage and temperature are referred to as the PVT variables).As illustrated in FIG. 4, if the first bias signal VBIAS1 is applied tothe gate terminals of the first and second bias transistors M_BIAS1 421and M_BIAS2 441, the semiconductor device can be less influenced byvariation in the PVT variables.

If delay cells are constructed using differential amplifiers, such asthose illustrated in FIG. 4, a DLL circuit having the delay cells canrobustly withstand variation in the PVT variables. For example, when thedelay cells are activated to operate, a user can apply the first biassignal VBIAS1 that goes high in order to bias the first and seconddifferential amplifiers 410 and 430.

A differential amplifier type delay cell has a good jitter performancewhen signal mixing is performed. The phase mixer 305 according to thepresent embodiment performs signal mixing by using the finely delayedsignal D_i received from the first delay circuit 310. Accordingly, sincesignal mixing is performed using a signal output from the differentialamplifier type delay cell having the good jitter performance, jitter inthe first internal clock signal Int_CLK can be reduced.

The first delay line 301 can include 2 or 3 first delay cells. For finelocking, a signal delay is controlled slightly several times since asmall number of delay cells are sufficient to perform fine locking. Thetotal number of differential amplifier type delay cells consuming alarge amount of power that are included in a DLL circuit according tothe present invention, is less than the total number of delay cellsincluded in the conventional delay circuit 110 illustrated in FIG. 1,thereby minimizing power consumption. That is, the DLL circuit accordingto the present embodiment includes only 2 or 3 delay cells includingdifferential amplifiers that can robustly withstand disturbance eventhough they consume a large amount of power, thereby minimizing powerconsumption.

Also, as described above, the DLL circuit according to aspects of thepresent invention is less influenced by variation in PVT variables andhas a good jitter performance by biasing the differential amplifiers ofa delay cell.

FIG. 5 is a detailed circuit diagram of an embodiment of the seconddelay cells 332 and 334 of the second delay cells 332, 334, . . . , 336included in the second delay line 330 of the DLL circuit 300 illustratedin FIG. 3. The construction and operation of the first second delay cell332 will now be described, as an example. The second delay cell 332includes first and second inverters 521 and 523, first and secondinversion selection transistors MS_B1 511 and MS_B2 513, and first andsecond selection transistors MS_1 531 and MS_2 533.

The first inverter 521 receives a second input signal IN2 via an inputterminal thereof. An input terminal of the second inverter 523 isconnected to an output terminal of the first inverter 521, and a firstcoarse delay signal DCO_1 obtained by delaying the second input signalIN2 is output via an output terminal of the second inverter 523.

The drain and source terminals of the first selection transistor MS_1531 are respectively connected to a first bias terminal of the firstinverter 521 and a ground voltage source V_GND, and a second selectionsignal SEL2_1 is supplied to the gate of the first selection transistorMS_1 531. The drain and source terminals of the second selectiontransistor MS_2 533 are respectively connected to a first bias terminalof the second inverter 523 and the ground voltage source V_GND, and thesecond selection signal SEL2_1 is supplied to the gate of the secondselection transistor MS_2 533.

A first terminal of the first inversion selection transistor MS_B1 511is connected to a second bias terminal of the first inverter 521 and asecond terminal thereof is connected to a high voltage source V_DD, anda second inverted selection signal SELB2_1 is supplied to the gate ofthe first inversion selection transistor MS_B1 511. A first terminal ofthe second inversion selection transistor MS_B2 513 is connected to asecond bias terminal of the second inverter 523 and a second terminalthereof is connected to the high voltage source V_DD, and the secondinverted selection signal SELB2_1 is supplied to the gate of the firstinversion selection transistor MS_B1 513.

The second selection signal SEL2_1 is determined to be at logic high orlogic low according to the result of phase comparison performed by thephase detection and control unit 340. It is assumed that a signal isdelayed by a time t1 whenever the signal passes through one delay cell.If a delay time is roughly t1, the second selection signal SEL2_1 thatgoes high is applied only to the first second delay cell 332, and secondselection signals SEL2_2 through SEL2_n that go low are applied to theother second delay cells 334, . . . , 336. Then only the first seconddelay cell 332 operates causing the delay time t1. Here, the secondinversion selection signal SELB2_1 is obtained by inverting the phase ofthe second selection signal SEL2_1.

The total number of delay cells included in the second delay line 330varies according to the frequency or period of a signal used. The rangeof delay time in a delay line can be equal to half the period of thesignal used. That is, if the phase of an internal clock signal iscontrolled based on the phase of an external clock signal, the internalclock signal can delayed for half the period thereof in a positiveleading direction and a negative lagging direction. For example, if halfa period of a signal is 10×t1, the second delay line 330 can include 10delay cells.

The operations and structures of the second delay cell 334 of FIG. 5 arethe same as those of the second delay cell 332, and thus a detaileddescription thereof will be omitted.

FIG. 6 is a graph illustrating the result of an experiment comparing theamount of current consumed in a DLL circuit according to the presentinvention with the amount of current consumed in a conventional DLLcircuit. Referring to FIG. 6, the amount of current consumed by the DLLcircuit according to the present embodiment is smaller by roughly 4 to 5mA than the amount of current consumed by the conventional DLL circuit.In FIG. 6, an average amount of current consumed can vary according tothe scale of a circuit used and the total number of delay cells includedin the circuit. That is, the average amount of current does not have afixed value and thus is indicated with “A” in FIG. 6.

If the amount of current consumed in a high-frequency domain has a smallvalue, the period of a signal is short in the high-frequency domain,that is, the range of maximum delay time is reduced. Thus, it issufficient to activate only a small number of delay cells, therebyreducing the amount of current consumed. In contrast, if the amount ofcurrent consumed in a low-frequency domain has a large value, the periodof a signal is long in the low-frequency domain, that is, the range ofmaximum delay time is increased. Accordingly, a large number of delaycells needs to be activated, thereby increasing the amount of currentconsumed.

As described above, a DLL circuit according to aspects of the presentinvention performs coarse locking and fine locking by using differenttype delay cells, and thus consumes a small amount of power and robustlywithstands jitter and variation in the PVT variables.

While embodiments in accordance with the present invention has beenparticularly shown and described with reference to exemplary embodimentsthereof, it will be understood by those of ordinary skill in the artthat various changes in form and details can be made therein withoutdeparting from the spirit and scope of the present invention as definedby the following claims.

1. A delay locked loop circuit comprising: a first delay line configuredto delay a received external clock signal for a fine delay time and thenoutput a first internal clock signal a second delay line configured todelay a second clock signal for a coarse delay time and then output asecond internal clock signal; and a phase detection and control unitconfigured to detect a difference between the phases of the externalclock signal and the second internal clock signal, and to control thefine delay time and the coarse delay time, wherein the first delay lineand the second delay line are sequentially arranged, and the secondclock signal is generated using the first internal clock signal, whereina type of a delay cell of the first delay line is different from a typeof a delay cell of the second delay line, wherein the type of delay cellis defined by an amount of delay time produced by the delay cell, andwherein the first delay line comprises: a first delay circuit includingn delay cells connected in series; and a phase mixer configured toselect at least one of the external clock signal and first through nthfinely delayed signals and then output a signal generated by using theselected signal as the first internal clock signal, in response toinformation regarding the detected phase difference and an output of thephase detection and control unit.
 2. The delay locked loop circuit ofclaim 1, wherein a delay cell of the first delay line comprises adifferential amplifier.
 3. The delay locked loop circuit of claim 1,wherein a delay cell of the second delay line comprises an inverter. 4.The delay locked loop circuit of claim 1, further comprising a replicadelay path arranged between an output terminal of the second delay lineand the phase detection and control unit, and configured to compensatefor a delay occurring during transmission of the second internal clocksignal to a target circuit which uses the second internal clock signal.5. The delay locked loop circuit of claim 1, wherein the first delayline includes a number of delay cells in a range of 2 through
 5. 6. Thedelay locked loop circuit of claim 5, wherein an ith delay cell in thefirst delay line comprises: a first differential amplifier configured torespectively receive the (i−1)th finely delayed signal output from an(i−1)th delay cell in the first delay line and an inverted signal of the(i−1)th finely delayed signal via two input terminals of the firstdifferential amplifier, differentially amplify the (i−1)th finelydelayed signal and the inverted signal of the (i−1)th finely delayedsignal, and then output the amplified signals; and a second differentialamplifier configured to respectively receive the amplified signals fromboth output terminals of the first differential amplifier via two inputterminals of the second differential amplifier, differentially amplifythe amplified signals, and then output the ith finely delayed signal andan inverted signal of the ith finely delayed signal via both outputterminals of the second differential amplifier, wherein the first andsecond differential amplifiers operate in response to a first selectionsignal.
 7. The delay locked loop circuit of claim 6, wherein the phasedetection and control unit is configured to perform a phase comparisonto determine if the first selection signal is at a logic high or logiclow.
 8. The delay locked loop circuit of claim 6, wherein the firstdifferential amplifier of the ith delay cell comprises: a first MOStransistor having a drain connected to a power supply source configuredto supply a high voltage, and configured to receive the (i−1)th finelydelayed signal via a gate thereof; a first inversion MOS transistorhaving a drain connected to the power supply source, and configured toreceive the inverted signal of the (i−1)th finely delayed signal via agate thereof; a first selection MOS transistor having a drain connectedto a source of the first MOS transistor, and configured to receive thefirst selection signal via a gate thereof; and a first bias transistorhaving a drain connected to the first selection transistor and a sourceconnected to a ground voltage source, and configured to receive a firstbias signal via a gate thereof, wherein the second differentialamplifier of the ith cell of the first delay cells comprises: a secondMOS transistor having a drain connected to the power supply source and agate connected to the drain of the first MOS transistor, and configuredto output the ith finely delayed signal via the drain of the second MOStransistor; a second inversion MOS transistor having a drain connectedto the power supply source and a gate connected to the drain of thefirst inversion MOS transistor, and configured to output the invertedsignal of the ith finely delayed signal via the drain of the second MOStransistor; a second selection MOS transistor having a drain connectedto the source of each of the second MOS transistors, and configured toreceive the first selection signal via a gate of the second selectionMOS transistor; and a second bias transistor having a drain connected tothe source of the second selection MOS transistor and a source connectedto the ground voltage source, and configured to receive the first biassignal via a gate of the second bias transistor.
 9. The delay lockedloop circuit of claim 8, wherein the first bias signal is supplied inorder to bias the first and second differential amplifiers.
 10. Thedelay locked loop circuit of claim 8, wherein the first differentialamplifier of the ith delay cell further comprises: a first resistorconnected between the drain of the first MOS transistor and the powersupply source; and a second resistor connected between the drain of thefirst inversion MOS transistor and the power supply source, wherein thesecond differential amplifier of the ith cell of the first delay cellsfurther comprises: a third resistor connected between the drain of thesecond MOS transistor and the power supply; and a fourth resistorconnected between the drain of the second inversion MOS transistor andthe power supply source.
 11. The delay locked loop circuit of claim 1,wherein a kth delay cell in the second delay line comprises: a firstinverter configured to receive a signal output from a (k−1)th delaycell; and a second inverter having an input terminal connected to anoutput terminal of the first inverter, and configured to output a kthcoarsely delayed signal via an output terminal thereof.
 12. The delaylocked loop circuit of claim 11, wherein the kth delay cell comprises:the first inverter having an input terminal connected to an outputterminal of a second inverter of the (k−1) cell of the second delayline, and an output terminal connected to the input terminal of thesecond inverter of the kth cell of the second delay line; the secondinverter configured to output the kth coarsely delayed signal via anoutput terminal thereof; a first inversion selection transistor having afirst terminal connected to the power supply source and a secondterminal connected to a first bias terminal of the first inverter, andconfigured to receive an inverted signal of a second selection signalvia a gate thereof; a first selection transistor having a first terminalconnected to a second bias terminal of the first inverter and a secondterminal connected to the ground voltage source, and configured toreceive the second selection signal via a gate thereof; a secondinversion selection transistor having a first terminal connected to thepower supply source and a second terminal connected to a first biasterminal of the second inverter, and configured to receive the invertedsignal of the second selection signal via a gate thereof; and a secondselection transistor having a first terminal connected to a second biasterminal of the second inverter and a second terminal connected to theground voltage source, and configured to receive the second selectionsignal via a gate thereof.
 13. The delay locked loop circuit of claim12, wherein the first and second inverters are configured to operate inresponse to the second selection signal.
 14. The delay locked loopcircuit of claim 13, wherein the phase detection and control unit isconfigured to perform a phase comparison to determine if the secondselection signal is at a logic high or logic low.
 15. A delay lockedloop circuit, comprising: a first delay line configured to delay areceived external clock signal for a fine delay time and then output afirst internal clock signal; a duty cycle correction unit configured tocorrect a duty cycle of the first internal clock signal and then outputa second clock signal; and a second delay line configured to delay thesecond clock signal for a coarse delay time and then output a secondinternal clock signal, wherein the first delay line and the second delayline are sequentially arranged, and the second clock signal is generatedusing the first internal clock signal, wherein a type of a delay cell ofthe first delay line is different from a type of a delay cell of thesecond delay line, and wherein the type of delay cell is defined by anamount of delay time produced by the delay cell.
 16. The delay lockedloop circuit of claim 15, wherein the duty cycle correction unitcomprises: a charge pump configured to output a control signalconfigured to correct a duty cycle of the first internal clock signal toan amplification unit, in response to the second internal clock signal;the amplification unit configured to compensate for the duty cycle ofthe first internal clock signal and to output the second clock signal,in response to the control signal; and a digital-to-analog converterconfigured to transform information regarding a duty cycle of the secondinternal clock signal into a digital signal and then store the digitalsignal, for a memory device power down mode.